Noise from HDMI port, Pi2, HiFiBerry DAC+ [SOLVED]

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Noise from HDMI port, Pi2, HiFiBerry DAC+ [SOLVED]

Postby PeteB » 19 May 2016, 05:24

Edit (6-6-2016): Time to put this to rest... :D

*****

I've had some issues with noise on the outputs of the DAC+. I was finally able to trace it to noise conducted over the HDMI port when the cable is connected. I would be grateful for any information or links on how to keep this from happening.

With the HDMI cable, I get around 80db in actual use, equivalent to 14-bit useful resolution. Without the cable I get close to the expected 100~110 db dynamic range. I would like to do better.

See below for some screen grabs from RMAA. I also have similar results from another tool called "Daquarta" I can post later.

The DAC+ results are very good, when tested with the HDMI cable unplugged, so I do not suspect a hardware problem.

In the pics, the white trace is a test with HDMI unplugged. The green trace shows the effects of the noise with HDMI connected. The graphs are on a logarithmic scale, so the difference does not look like much, but it is significant.

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Last edited by PeteB on 06 Jun 2016, 16:48, edited 1 time in total.
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby dunghnguyen » 19 May 2016, 06:46

I am not fully aware what you have done on the analysis but it looks meaningful for the improvement (if any). For me, I just don't plug the HDMI haha... I love Rune with DAC+ a lot...its sounds are really nice :)
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby hondagx35 » 19 May 2016, 11:57

Hi Pete,

is this with a regular monitor or TV plugged in the HDMI?
I'm asking, because with my small TFTs (waveshare, ODROID) i can't measure any noise.

Frank
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby PeteB » 19 May 2016, 14:46

@dungnguyen: I have recorded amazingly good results with the DAC+, when under ideal conditions, and when testing at 44.1K, 48K, 96K (I have nothing that will reliably measure above that). Unfortunately, there is this noise susceptibility, which can sometimes make the test results much worse.

@Frank: I do not own any small TFTs. In this test I used an LCD TV. Other tests with a new-ish Viewsonic HDMI LED monitor were similar. I believe the HDMI is conducting noise from other sources (note the peak at 60Hz - well, 50Hz in your case). The TV/monitor is only a small contributor to the noise. This can be shown by leaving the TV connected to power and to the HDMI port, and disconnecting or turning off everything else.
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby dunghnguyen » 20 May 2016, 10:56

@PeteB: thanks for your analysis as well as advice. For my ear, I cannot recognize any noise with or without hdmi port connected. Thanks God for that so that I can still listen DAC+ ...I luv it much ...play from Pi 2 signal out via USB to DAC SMSL M8 decoded perfectly.
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby rikardo1979 » 20 May 2016, 11:34

always use good quality cables ;) All this is comming from your cable as its like an long aerial
>>>Please always follow rules and read before you post<<<
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby PeteB » 20 May 2016, 14:09

rikardo1979 wrote:.... All this is coming from your cable as its like an long aerial

Not in this case. You are correct about using good cables of course, but the noise is not RFI or EMI (I tested for that).

Here is why I know how the noise is being conducted by the HDMI cable:

If I disconnect the cable at either end, the noise goes away. Same result if I leave the cable connected and the TV (or monitor) turned on and plugged into the wall socket, and I simply turn off or unplug all possible noise sources. If the cable acted like an aerial, akin to an un-terminated scope probe for example, then some noise would remain if I left the cable connected to the pi, and disconnected at the TV. The noise would also change if I moved the cable, or if I made a loop and rotated it.

It is definitely noise from various sources, conducted over the HDMI cable and through the HDMI connector. I can induce varying amounts of noise. With all noise sources removed, the results are quite good.

With RMAA and a 24-bit sound card input, 0.004% THD and -100db A-weighted noise is at the limit of the hardware.

With calibrated inputs and better software, I can measure down to 0.002% THD (0.001% would be perfect score for the DAC+).
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THD and noise, HiFiBerry DAC+ RCA, under ideal conditions

Postby PeteB » 20 May 2016, 15:19

Test with an external USB 24-bit soundcard, and software calibrated to the sound card inputs:

Image

Test conditions:
--------------------
test signal: 984.350Hz, 48KHz-16 bit wav file, 50% FS, 1.01Vrms measured at the DAC+ output
source: RuneAudio, HW volume control (or disabled) at 100, HiFiBerry DAC+ I2S
input: SB X-Fi HD, ~12k-ohm impedance, 96K-24bit resolution
software: Daquarta for Windows v9.10, calibrated to sound card inputs at 1V rms

Disclaimer: Everything was adjusted to give the best results. Distortion and noise would be higher in normal use, with normal recorded music, and at normal listening volumes.

@Rikardo: Same interconnect cables used for this test, except HDMI cable NOT plugged, and a shorter better quality RCA cable (still under $10... :mrgreen: )

@dunghnguyen: If you keep noise sources away from your Pi, and use your battery bank with no connections to the mains except your power amp, you should be able to come close to the same low noise and THD.
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby rikardo1979 » 20 May 2016, 17:29

PeteB wrote:
rikardo1979 wrote:.... All this is coming from your cable as its like an long aerial

Not in this case. You are correct about using good cables of course, but the noise is not RFI or EMI (I tested for that).

Here is why I know how the noise is being conducted by the HDMI cable:

If I disconnect the cable at either end, the noise goes away. Same result if I leave the cable connected and the TV (or monitor) turned on and plugged into the wall socket, and I simply turn off or unplug all possible noise sources. If the cable acted like an aerial, akin to an un-terminated scope probe for example, then some noise would remain if I left the cable connected to the pi, and disconnected at the TV. The noise would also change if I moved the cable, or if I made a loop and rotated it.

It is definitely noise from various sources, conducted over the HDMI cable and through the HDMI connector. I can induce varying amounts of noise. With all noise sources removed, the results are quite good.

With RMAA and a 24-bit sound card input, 0.004% THD and -100db A-weighted noise is at the limit of the hardware.

With calibrated inputs and better software, I can measure down to 0.002% THD (0.001% would be perfect score for the DAC+).

in this case you have few options

  • get new TV which dont push noise over HDMI - very expensive option
  • dont use HDMI in HiFi - highly recommended
  • dont use this measuring software, so you would not know (if the noise is not audible) - best solution
>>>Please always follow rules and read before you post<<<
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Re: Noise from HDMI port, Pi2, HiFiBerry DAC+

Postby PeteB » 20 May 2016, 20:19

rikardo1979 wrote:
  • get new TV which dont push noise over HDMI - very expensive option
  • dont use HDMI in HiFi - highly recommended
  • dont use this measuring software, so you would not know (if the noise is not audible) - best solution


Hi Rikardo,

    1 - I tried only the one TV, but a couple HDMI monitors, same results.
    2 - Yes, I really prefer headless anyway, and I am looking into a 2-line display.
    3 - Bbbbut: my other software is even more sensitive than this middlin' sound card! How can I live with myself if I don't solve this? :lol:

Ok, seriously, it is audible with plain vanilla 55-ohm AKG headphones, and a middling headphone amp, IF I use the hardware volume control at normal listening levels. If I don't, not audible, so I can make it go away by pushing the noise down. Still, it is annoying to be limited to about 14 bits resolution when you are playing 24-bit material... :roll:

The best solution for now is to keep all noise sources away. The TV is not the source, the HDMI is just the conduit to the noise. If you look at the graphs above closely, you will notice a 60 Hz (mains freq) peak on the green trace. By contrast my rotating disk drive only adds a tiny bit of noise, and the stock p/s only a little bit more.

edit:

Anyway, this is supposed to be a software forum, so I will do my best to stick to that from now on... :D
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